JP2011-106377A discloses an engine configuration with respect to a positional relation between a spark plug and an injector disposed in a combustion chamber, and a control method by using the spark plug and the injector based on the engine configuration. In the engine configuration, a distance from a center position of a discharge gap of the spark plug to a center position of the injection hole which is closest to the spark plug and a distance from the center position of the discharge gap to a center axis of the fuel spray which is injected from the injection hole are set within a specific range, respectively.
The control method based on the engine configuration is to apply a high voltage to the spark plug over a fuel injection period after a lapse of a predetermined time from the start of fuel injection from the injector. The fuel injected from the injector under high pressure forms a low pressure part by taking away the surrounding air (entrainment). According to such control method, the low pressure part is formed to which the discharge spark generated in the discharge gap is attracted. Therefore, an ignitability of the air-fuel mixture formed around the spark plug can be improved.
In addition, JP2011-106377A discloses an activation of an exhaust gas cleaning catalyst at engine start as an application example of the attraction action described above. Although JP2011-106377A does not refer to, the activation of the exhaust gas cleaning catalyst is generally performed by setting an ignition period (that is, a discharge period of the high voltage to the spark plug) on a retard side relative to the compression top dead center. Therefore, an activation control to which an attraction action is applied means an engine control in which the fuel injection period is overlapped with the ignition period which is set on the retard side relative to the compression top dead center.
The activation control has a potential to improve an ignitability of the air-fuel mixture formed around the spark plug. However, combustion state at the engine start during which the activation control is performed is generally liable to be unstable. Therefore, when such an unstable state occurs frequently in the combustion cycles, combustion fluctuation between cycles increase to affect performance of the engine.
The present disclosure addresses the above described problem, and an object of the present disclosure is to suppress the combustion fluctuation between cycles when an engine control in which the injection period of the injector is overlapped with the discharge period of the high voltage to the spark plug is applied to the activation of the exhaust gas cleaning catalyst.
The present disclosure provides a control device for an internal combustion engine. The control device is configured to control an internal combustion engine comprising an injector, a spark plug, a first intake valve, a second intake valve, a variable valve mechanism and an exhaust cleaning catalyst.
The injector is provided in an upper portion of a combustion chamber. The injector is configured to inject fuel from multiple injection holes into a cylinder directly.
The spark plug is provided at the upper portion of the combustion chamber. The spark plug is configured to ignite an air-fuel mixture inside the cylinder by using a discharge spark. The spark plug is also provided on a downstream side relative to the closest fuel spray to the spark plug among the fuel sprays injected from the multiple injection holes. The spark plug is also provided on an upper side of the combustion chamber relative to a contour surface of the closest fuel spray.
Each of the first intake valve and the second intake valve is configured to open and close the combustion chamber.
The variable valve mechanism is configured to increase or decrease lift amount of any one of the first intake valve and the second intake valve.
The exhaust cleaning catalyst is configured to clean exhaust gas from the combustion chamber.
The control device is configured to control the spark plug and the injector as an activation control of the exhaust cleaning catalyst. In the activation control, the spark plug is controlled so as to generate the discharge spark over an ignition period on a retard side of compression top dead center whereas the injector is controlled so as to perform a first injection on an advance side of the compression top dead center and a second injection on the retard side of the compression top dead center which overlaps with at least a part of the ignition period.
The control device is also configured to control the variable valve mechanism as the activation control of the exhaust cleaning catalyst. In the activation control, the variable valve mechanism is controlled so that swirl flow due to a difference in lift amount between the first intake valve and the second intake valve is generated in the combustion chamber. When a parameter relevant to combustion fluctuation between cycles of the activation control is determined to exceed a threshold, the variable valve mechanism is also controlled so that the difference in lift amount is enlarged in comparison to a case where the parameter is determined to be less than the threshold.
When the discharge spark is generated from the spark plug, an intimal flame is generated the injected fuel of the first injection and the discharge spark. When the second injection is performed, the initial flame is attracted or both of the initial flame and the discharge spark are attracted to the closest fuel spray to the spark plug. When the attraction action of the initial flame or the discharge spark is weaken, the parameter relevant to combustion fluctuation between cycles is changed to increase. In this regard, when the difference in lift amount between the first intake valve and the second intake valve is enlarged, the swirl flow generated in the combustion chamber is enhanced. Therefore, when the parameter is determined to exceed the threshold, such a situation is eliminated by the valve control in which the swirl flow is enhanced.
In the control device for an internal combustion engine according to the present disclosure, the closest fuel spray to the spark plug may be injected on a downstream side relative to a flow direction of the swirl flow generated in the combustion chamber as viewed from the spark plug.
The spark plug is provided on the downstream side relative to the closest fuel spray to the spark plug among the fuel sprays injected from the multiple injection holes. Therefore, when the closest fuel spray to the spark plug is injected on the downstream side relative to the flow direction of the swirl flow generated in the combustion chamber as viewed from the spark plug, the initial flame or the discharge spark is efficiently attracted to the closest fuel spray to the spark plug.
In the control device for an internal combustion engine according to the present disclosure, diameter of an injection hole which is configured to inject the closest fuel spray to the spark plug may be larger than any diameter of the other injection holes which are configured to inject fuel sprays except for the closest fuel spray.
The spark plug is provided on the downstream side relative to the closest fuel spray to the spark plug among the fuel sprays injected from the multiple injection holes. Therefore, when the diameter of the injection hole which is configured to inject the closest fuel spray to the spark plug is larger than any diameter of the other injection holes, the initial flame or the discharge spark is efficiently attracted to the closest fuel spray to the spark plug.
As mentioned above, according to the control device of the present disclosure, it is possible to suppress the combustion fluctuation between cycles when the engine control in which the injection period of the injector is overlapped with the discharge period of the high voltage to the spark plug is applied to the activation of the exhaust gas cleaning catalyst.